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But expected warmer temperatures, low humidity and winds of up to 30 mph could increase fire activity this week, state fire spokesman Capt. Tom Piranio said.

"This could set up some potential fire growth similar to what we experienced when it grew exponentially last week," Piranio said. "We are working very aggressively to maintain the contingency lines."

Last week, the blaze grew to 111 square miles overnight when winds surged to more than 25 mph, the state forestry and fire protection department reported.

More than 5,000 firefighters -- from as far as Florida and Alaska -- have worked around the clock to increase the fire containment from 10 to 18 percent by Monday.

But a red flag warning has been issued for Tuesday as gusty winds could reach up to 35 mph by Wednesday.

The wildfire, which started on Sept. 13, continues to threaten about 21,000 structures, more than half of them homes.

It has destroyed at least 10 homes and 22 outbuildings in the White Meadows area of Pollock Pines, according to preliminary figures released Sunday.

About 100 evacuees were allowed to return home, but some 2,700 remain under evacuation orders, state fire spokesman Daniel Berlant said. The fire also continued to threaten a key University of California, Berkeley research station that is home to scores of experiments on trees, plants and other wildlife.

Meanwhile, thick smoke from the fire resulted in another day of school closures in the Pollock Pines area.

Colfax Elementary School, Colfax High School and Sierra Hills Elementary in Placer County were all closed Monday. Foresthill High School and Foresthill Divide School were closed due to poor air quality.

Placer County public health officials said that a smoke-related advisory will stay in effect for Monday. Public health officials are consulting with school districts to help them determine whether schools should remain open in the impacted areas.

On Sunday, poor air quality forced a last-minute cancellation of two popular Ironman events in nearby Lake Tahoe, disappointing about 3,000 athletes who signed up for the competition, Ironman operations manager Keats McGonigal said.

There will be two community meetings held Monday to update residents on the King Fire.

One of the meetings will be located at Golden Sierra High School at 5105 Garden Valley Road in Garden Valley. The second will be located at the fire's evacuation center at the Seventh-day Adventist Church in Camino.

A man charged with starting the fire, Wayne Allen Huntsman, 37, pleaded not guilty to arson Friday and remains in the El Dorado County jail on $10 million bail.